Process using flue gas heat for pyrolysis and drying of organic material

ABSTRACT

A process for pyrolysis and drying of an organic material, comprising: pyrolyzing the organic material to generate a coke; combusting the coke in a regenerator to produce a flue gas; cooling the flue gas from the regenerator by mixing the flue gas with an air to produce a cooled flue gas; and channeling the cooled flue gas to a heat exchanger to assist in drying a wet organic material being conveyed on a conveyor belt, wherein the conveyor belt is operably connected to a pyrolysis unit used for the pyrolyzing and the conveyor belt is in thermal communication with the heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser. No. 13/623,656, filed Sep. 20, 2012. U.S. patent application Ser. No. 13/623,656 claims priority under 35 USC §119(e) to provisional patent application Ser. No. 61/537,467 filed Sep. 21, 2011, both of which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to the pyrolysis of organic material and combustion of coke, and more particularly to use of the resulting combustion gases to dry additional organic material. Still more particularly, the present invention relates to the cooling of combustion gas left over from a pyrolysis process to make the gas suitable for transfer to a heat exchange dryer.

BACKGROUND AND SUMMARY

Pyrolysis is a process of thermochemical decomposition of an organic material, such as biomass, at high temperatures and usually in the absence of substantial amounts of oxygen. Pyrolysis systems are useful because they are capable of taking a feed stream of raw organic material, and converting that material to, for example, coke, oil, and/or other byproducts.

The feed stream of organic material that is input to a pyrolysis system usually should be properly prepared. This preparation may include drying of the organic material if the organic material comprises too much moisture, i.e., an amount that may interfere or inhibit processing. This varies, of course, with the specific organic material but in some instances raw organic material may contains more than about 10% moisture, and often as high as 50% moisture depending upon its source. In many instances the moisture content of the material should be lowered to about 10% or less before subjugation to a pyrolysis reaction. This often assists in reducing or substantially eliminating the formation of a tar-like substance that may inhibit and/or interfere with further processing.

There are multiple ways of drying organic material. One way is through the use of drum dryers. Another is using heat exchangers. One advantage to using heat exchangers, rather than drum dryers, is that heat exchangers may assist in reducing volatile organic compound (VOC) emissions that ultimately enter the environment. In some instances a dryer arrangement may include a conveyor belt that conveys the organic material past one, two, or even a series of heat exchangers that dry the organic material. Such an arrangement requires a constant supply of heated gas to the heat exchangers.

After the organic material has been dried, it may be subjected to pyrolysis which typically produces compositions comprising, for example, one or more of coke, gaseous products, and/or oil. The coke is typically introduced to a regenerator, where it is combusted, to form a flue gas. Due to the high heat required for the pyrolysis reaction, and the additional heat added during combustion, the flue gas may leave the regenerator at a very high temperature, often as high as 1200° F. or more.

Accordingly, many pyrolysis systems share two common features. First, they require that the raw organic material be dried prior to the pyrolysis reaction, and second, one byproduct of the process is hot regenerator flue gas. Efficiency may be gained, therefore, by drying the raw organic material using the hot regenerator flue gas. This may be achieved by using heat exchangers, as discussed above, where the gas supplied to the heat exchangers is the regenerator flue gas.

One problem with this arrangement, however, is that in some cases safety considerations prevent the transfer of the very high temperature regenerator flue gas to the heat exchangers in common gas lines, such as carbon steel gas lines. Instead, the pipework interconnecting the pyrolysis regenerator and the heat exchanger must be constructed of more expensive materials that are rated to more safely carry very high temperature gas, such as, for example, stainless steel. This requirement adds additional cost since often the regenerator may be separated from the heat exchangers by up to several hundred feet or more.

In one embodiment, the present invention provides a system that includes a pyrolysis unit for pyrolyzing organic material to produce a composition comprising at least pyrolysis oil and coke, a regenerator unit to combust at least a portion of the coke and produce a regenerator flue gas, and a mixer connected to the regenerator unit to mix the regenerator flue gas with air to produce a cooled flue gas. The system may further include at least one heat exchanger connected to the mixer to extract heat from the cooled flue gas, and a conveyer belt in thermal communication with the at least one heat exchanger and operably connected to the pyrolysis unit. The conveyer belt can convey organic material in need of drying past the at least one heat exchanger to dry the organic material.

A variant of or addition to this system may include a pyrolysis unit employing a heat transfer medium such as a particulate source of heat like sand, wherein the pyrolyzing unit pyrolyzes biomass to form a mixture comprising at least pyrolysis oil, coke, and heated particulate source like sand, and wherein the unit has an outlet to transfer the coke and heated particulate source like sand. The system also may include a regenerator operably connected to the outlet of the pyrolysis unit to receive the coke and heated particulate source like sand, wherein the regenerator combusts the coke to a regenerator flue gas and transfers at least a portion of the particulate source like sand back into the pyrolysis unit, and a mixer operably connected to the regenerator to receive the regenerator flue gas and mix the regenerator flue gas with ambient air to produce a cooled flue gas. In addition, the system includes at least one heat exchanger operably connected to the mixer to use the cooled flue gas to dry biomass in need of drying.

In one embodiment the present invention also provides a process for pyrolysis and drying of organic material, including the steps of pyrolyzing organic material to generate at least pyrolysis oil and coke, combusting the coke in a regenerator to produce flue gas, cooling flue gas from the regenerator by mixing the flue gas with air, and channeling the cooled flue gas to a heat exchanger to assist in drying wet organic material.

BRIEF DESCRIPTION OF THE DRAWING

A more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawing in which:

FIG. 1 is a diagram of an integrated pyrolysis regenerator and biomass dryer according to one specific embodiment of the present invention.

DETAILED DESCRIPTION

In general terms one embodiment of the present invention pertains to a process for pyrolysis and drying of organic material. The organic material may be any suitable material that is capable of being pyrolyzed. The type of material selected may, of course, vary depending upon, for example, the desired products and/or their desired use. Since in one embodiment the present invention also assists in drying the starting organic materials, the present invention may be most advantageous when pyrolyzing materials that may need to be at least partially dried before undergoing pyrolysis. Such materials may include, for example, coal, biomass, and/or mixtures thereof.

Typically, useful biomass includes any cellulosic or lignocellulosic material and includes materials comprising cellulose, and optionally further comprising hemicellulose, lignin, starch, oligosaccharides and/or monosaccharides. Biomass may also comprise additional components, such as protein and/or lipid. Biomass may be derived from a single source, or biomass can comprise a mixture derived from more than one source; for example, biomass could comprise a mixture of corn cobs and corn stover, or a mixture of grass and leaves. Biomass includes, but is not limited to, bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, sludge from paper manufacture, yard waste, wood and forestry waste. Examples of biomass include, but are not limited to, corn grain, corn cobs, crop residues such as corn husks, corn stover, grasses, wheat, wheat straw, barley, barley straw, hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers and/or animal manure.

The organic material is pyrolyzed under any convenient conditions to form coke and/or byproducts such as oils. The pyrolysis conditions such as time and pressure may vary depending upon the specific organic material and desired products. Typically, the material is heated in a pyrolysis unit at atmospheric pressure or under pressure at a temperature and time suitable to form coke. Such pyrolysis temperatures vary depending upon the material but often are above about 800F. Typically, the pyrolysis is conducted in the substantial absence of oxygen and/or water.

While any suitable pyrolysis unit may be employed, in one embodiment a pyrolysis unit is employed wherein a solid particulate may be used as a heat transfer media is used when pyrolyzing the organic material. Any convenient particulate source of heat may be employed so long as it does not substantially inhibit or interfere with the process. In some instances, such particulate sources of heat are employed in, for example, the manner of a fluidized bed. The precise type of particulate source of heat is not critical. However, it may be advantageous in some situations to employ a particulate source of heat which can be recycled, e.g. by transferring it to a regenerator with the coke and then returning at least a portion of the particulate source to the pyrolysis unit for reuse in pyrolyzing additional organic material. Such particulate sources of heat are widely available and include, for example, silicas, aluminas, and the like. In one embodiment, at least a portion of the particulate sources of heat comprises, for example, sand. Additionally or alternatively, the particulate source or a portion of it may be separated from the coke within the pyrolysis unit.

At least a portion of the coke may be combusted in any convenient manner to produce flue gas. Typically, the coke is combusted in a regenerator unit. The specific composition of the resulting regenerator flue gas will vary depending upon the starting material, pyrolysis conditions, and combustion conditions. That is, the flue gas will vary in amount of nitrogen, carbon dioxide, water, and/or other components. Advantageously, the flue gas will have very little to substantially no volatile organic compounds when, for example, conveyer drying as opposed to drum drying is employed.

The flue gas will usually be very hot, e.g. above 900F or above 1000F, due to the pyrolysis and combustion conditions. If it is desired to transport the flue gas through, for example, carbon steel lines then it may be advantageous to quench or cool it. The temperature to which it should be cooled and the method used to do it will necessarily vary depending upon its initial composition, temperature, and/or equipment employed. In one embodiment, the flue gas is cooled by mixing the flue gas with a fluid such as air, e.g., ambient or even cooled air. This may usually be accomplished in a mixer connected to or even within the regenerator unit to generate a cooled flue gas which may then be transported via, for example, the carbon steel lines.

The cooled or quenched flue gas advantageously still has a substantial amount of useful heat. Accordingly, the heat may still be used advantageously in any convenient manner to assist in drying organic material in need of such drying. In one embodiment, the gas is channeled to a heat exchanger of a dryer to assist in drying, for example, wet biomass. The wet biomass may be conveyed along a conveyer belt in thermal communication with the at least one heat exchanger and operably connected to the pyrolysis unit. In this manner, the wet biomass in need of drying is conveyed past the at least one heat exchanger may be made useful as a feed to the pyrolysis unit.

Referring now to the drawing, wherein like reference numerals indicate similar features, there is shown in FIG. 1 a diagrammatic overview of one possible system. According to the system, an organic material may be fed into a pyrolysis unit 10. Preferably, the organic material introduced to the pyrolysis unit 10 has a moisture content of about 10% by weight or less. Although it is possible to pyrolyze organic material having a moisture content of greater than about 10% by weight, and the present invention contemplates pyrolyzing such material, this can lead to problems due to evaporation of moisture from the organic material within the pyrolysis unit 10. Such evaporation within the pyrolysis unit may lead to lower temperatures and partially impair the pyrolysis reaction. The organic material may be any carbon-based organic material, such as, for example, biomass, coal, etc.

The pyrolysis unit 10 contains a heat transfer medium which may be a solid particulate, such as, for example, sand. Any solid heat transfer medium may be used within the pyrolysis unit 10, as long as it has the necessary properties to avoid breaking down under the high temperature conditions that exist within the pyrolysis unit 10 during the pyrolysis reaction. Upon entering the pyrolysis unit 10, the organic material is converted through a pyrolysis reaction into a plurality of components, including, for example, volatile compounds, such as CH₄, pyrolysis oil, and a typically solid residue called coke. Coke is typically composed mostly of carbon, but may also include hydrogen and other components. Typically, substantially all of the components except the coke and the heat transfer medium vaporize within the pyrolysis unit 10 and are separated from the coke and the heat transfer medium after the pyrolysis reaction. The coke may mix with the heat transfer medium in the pyrolysis unit 10 and exit the unit as a coke/heat transfer medium mixture. After exiting the pyrolysis unit 10, the volatile compounds and the pyrolysis oil, as well as any other byproducts of the pyrolysis reaction, may be collected or disposed of using conventional methods. The coke/heat transfer medium mixture may be fed into a regenerator unit 12.

The regenerator unit 12 is typically a cylinder or other suitable container that is configured to accept the coke/heat transfer medium mixture. In the regenerator unit 12, the coke/heat transfer medium mixture is mixed with air, which causes combustion of the coke, thereby producing a regenerator flue gas. Typically, the regenerator flue gas is composed mostly of nitrogen, but may also contain oxygen, carbon dioxide, and/or water vapor. The composition of the flue gas may vary depending on the organic material that has been pyrolyzed and other factors. After combustion, the heat transfer medium is preferably fed back into the pyrolysis unit 10 for reuse. The regenerator flue gas is transferred from the regenerator unit 12 to a mixer 14. Typically, the regenerator flue gas leaves the regenerator unit 12 at a high temperature, such as a temperature of up to about 1200° F. or higher. The regenerator flue gas is preferably transferred to the mixer 14 through transfer lines made of a material suitable for safely carrying high temperature gas, such as, for example, stainless steel.

In the mixer 14, the regenerator flue gas is mixed with air. The air may be provided to the mixer 14 by an air blower 16 and is preferably ambient air. As the air mixes with the regenerator flue gas in the mixer 14, the regenerator flue gas is cooled. In one preferred embodiment, the flue gas is cooled to a temperature of about 700° F. or less. The cooled flue gas is then transferred to at least one heat exchanger 20. One advantage of cooling the regenerator flue gas in the mixer 14 is that the cooled flue gas may be safely transported in gas lines 18 made of a material suitable for carrying lower temperature gases, such as carbon steel.

In one preferred embodiment, the heat exchangers 20 are positioned near a conveyer belt 22 so that the conveyor belt 22 is in thermal communication with the heat exchangers 20. Wet organic material is fed onto the conveyor belt 22 and then carried past the heat exchangers 20. As the wet organic material passes the heat exchangers 20, the moisture in the biomass evaporates into the air surrounding the organic material, thereby moistening the air and drying the organic material. At least one fan 24 may be positioned near the organic material on the conveyor belt and arranged to direct the moist air away from the organic material and out a vent (not shown). The dried organic material may then be fed into the pyrolysis unit 10.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention. 

What is claimed is:
 1. A process for pyrolysis and drying of an organic material, comprising: a. pyrolyzing the organic material to generate a coke; b. combusting the coke in a regenerator to produce a flue gas; c. cooling the flue gas from the regenerator by mixing the flue gas with an air to produce a cooled flue gas; and d. channeling the cooled flue gas to a heat exchanger to assist in drying a wet organic material being conveyed on a conveyor belt, wherein the conveyor belt is operably connected to a pyrolysis unit used for the pyrolyzing and the conveyor belt is in thermal communication with the heat exchanger.
 2. The process of claim 1, wherein a heat transfer media is used when pyrolyzing the organic material and the heat transfer media is transferred to the regenerator with the coke, the heat transfer media being a particulate source of heat.
 3. The process of claim 2, wherein the particulate source of heat comprises sand.
 4. The process of claim 2, wherein the regenerator returns the heat transfer media to a pyrolysis unit for reuse in pyrolyzing additional organic material.
 5. The process of claim 4, further comprising the step of feeding the organic material that has been dried into the pyrolysis unit.
 6. The process of claim 1, wherein the flue gas from the regenerator initially has a temperature of at least about 1000° F. before cooling.
 7. The process of claim 1, wherein the flue gas is cooled to about 700° F. or less.
 8. The process of claim 1, further comprising fanning a moist air away from the wet organic material being conveyed on the conveyor belt.
 9. The process of claim 1, wherein the wet organic material has a moisture content of greater than about 10% by weight when it enters the conveyor belt.
 10. The process of claim 1, wherein a dried organic material has a moisture content of less than about 10% by weight when it leaves the conveyor belt.
 11. The process of claim 1, wherein the air is ambient air.
 12. The process of claim 1, wherein the mixing is done in stainless steel transfer lines.
 13. The process of claim 1, wherein the channeling is done in carbon steel transfer lines.
 14. The process of claim 1, wherein the heat exchanger reduces volatile organic compound (VOC) emissions.
 15. The process of claim 1, wherein the heat exchanger comprises a series of heat exchangers.
 16. The process of claim 1, wherein the organic material comprises municipal solid waste. 